1. Field of the Invention
This invention relates to a flexible tool that is particularly adaptable for use as an endodontic instrument, most particularly, an endodontic reamer/file for use by practitioners in removing the pulpal material from an exposed root of a tooth and for shaping the root canal to receive filler material therein.
2. Background of the Invention
One of the most significant advancements in dentistry in recent years has been improved treatment of abscessed teeth. In the past a tooth, once abscessed, was usually pulled as the only remedy for alleviating the intense pain. By “abscessed” usually means that the root canal of the tooth becomes infected and the infection causes pressure on the tooth and the nerve endings associated therewith that result in, sometimes, almost unbearable pain. With the advent of endodontics the drastic measure of extracting a tooth that has become abscessed has been eliminated.
The first step in the endodontic treatment of an abscessed tooth is to drill an opening in the crown of the tooth to provide access to the root canal. Once the root canal is exposed, the practitioner then must thoroughly clean the root canal of pulpal material since if the pulpal material is not thoroughly and carefully removed it can be the source of continued infection. Not only is it necessary that the pulpal material be removed but the root canal usually must be shaped in such a way as to permit filling of the root canal with a filler material. While other types of filler materials have been provided still at the present time the most common filler is a paste-like material referred to as “gutta-percha.” If the canal is not properly cleaned and shaped the step of filling with gutta-percha, or other filler material, may leave void areas that invite the introduction into the root canal of organic matter that can be followed by bacterial action. For these reasons much of the effort of a practitioner to successfully accomplish the endodontic treatment of an abscessed tooth is the cleaning and shaping of the root canal. These steps are accomplished utilizing small diameter tapered reamer/files that are inserted by the practitioner through the exposed crown area into the root canal. The canal must be cleaned from the crownal area advancing to the root apex.
A root canal is typically in a tapered configuration, that is, the cross-sectional area of canals is usually greater near the crown of the tooth and is at a minimum at the apex of the tooth, that is, the distal end of the root canal. While the root canal is naturally tapered it is not tapered symmetrically and the canal can have inclusions in intermediate portions between the apex and the crown area that interfere with the passage of filler material. Therefore the root canal must be shaped to remove unnecessary intrusions and to improve the chances that the practitioner can successfully fill the root canal.
Files are usually provided with a small cylindrical plastic handle portion by which the practitioner manually manipulates the files. By “manipulation” means inserting a file into a canal and reciprocating it to file away intrusions and at the same time to remove pulpal material. Typically the practitioner inserts a file to the point of resistance and then rotates and reciprocates the file to engage spiral scraping edges with the canal wall. The file is then extracted to remove pulpal material and matter scraped from the wall. This procedure is repeated as necessary to clean the entire length of the canal. In the cleaning process the practitioner usually starts with a file of a small diameter and then, as progress is made in cleaning and shaping the canal, larger diameter files are employed until the root canal is shaped and cleaned to the apex. Accordingly, endodontic files usually come in sets of standard tapers and varying from smaller to larger diameters.
Instead of manually rotating an endodontic file the practitioner may insert the file proximal end into the chuck of a hand piece by which the file is mechanically rotated and manipulated.
Root canals are characteristically not straight. Some root canals curve more than others but few are perfectly straight from the crown to the apex. Therefore it is important that files be flexible so as to be able to follow the natural curvature of the root canal as it is cleaned and shaped from the tooth crown to the tooth apex. If a file is too stiff it can result in the file protruding through a side wall of a tooth root which can introduce an avenue of infection into the tooth. Further, if the file is stiff it is less successful in cleaning the entire area of a canal since the stiffness will cause the file to be deflected drastically to one side of a curve in a canal leaving a portion of the wall that defines the curve unexposed to the action of the file. Therefore, a high degree of flexibility is a desirable characteristic of an endodontic file.
In addition, the strength of a file is very important. In the process of reciprocating and rotating a file in a tooth it is possible for the file to break, leaving a broken part in the tooth. This creates a serious problem for the practitioner. Accordingly, it has long been a desire of the dental profession to have available dental files that are highly flexible and yet have strong torsional strengths to resist breakage as a result of the twisting and pulling actions as a file is manipulated within a root canal. The present invention provides a way of substantially decreasing the torque demand of dental files.
The introduction of nickel-titanium alloy for use in manufacturing endodontic instruments has greatly simplified root canal shaping procedures. Due to greater flexibility nickel-titanium has been found to be better than stainless steel in maintaining the original shape of files. Moreover, these instruments are also characterized by a larger maximum torque to failure than stainless instruments.
The nickel-titanium mechanically driven engine instrument operates turning continuously in a clock or counterclockwise direction. At the same time it is alternatively inserted and extracted from the root canals. The first working condition leads to the presence of a constant tangential stress whose maximum value depends on the canal anatomy and dentin hardness. In the second working condition, the instrument is constrained to follow the geometry of the root canals and is subjected to a normal stress that depends on the instrument cross section dimension and shape.
Normal stresses are responsible of the low cycle fatigue failure of instruments. The maximum tangential and normal stresses together are responsible for the ductile failure of instruments. The optimal design of an instrument cross section is extremely important because it directly influences its torsional and bending properties and, consequently, the maximum normal and tangential stress values.
3. Description of the Prior Art
For background information relating to the subject matter of this invention and specifically relating to dental reamer/files, reference may be had to the following issued United States patents and publications:
PATENTNUMBERINVENTOR(S)ISSUE DATETITLE4,443,193RoaneApr. 17, 1984Endodontic Instrument4,536,159RoaneAug. 20, 1985Endodontic Instrument4,934,934Arpaio, Jr. et al.Jun. 19, 1990Dental File/Reamer Instrument5,380,200Heath et al.Jan. 10, 1995Endodontic Instrument Of PredeterminedFlexibility5,464,362Heath et al.Nov. 7, 1995Endodontic Instrument5,658,145Maillefer et al.Aug. 19, 1997Set Of Instruments For Boring DentalRadicular Canals And Method Therefor5,692,902AebyDec. 2, 1997Set Of Instruments For The Boring OfRadicular Dental Canals5,873,719Calas et al.Feb. 23, 1999Dental Reamer5,897,316BuchananApr. 27, 1999Endodontic Treatment System5,921,775BuchananJul. 13, 1999Endodontic Treatment System5,975,899Badoz et al.Nov. 2, 1999Dental Reamer6,012,921RiitanoJan. 11, 2000Endodontic Systems For The Anatomical,Sectional And Progressive Corono-ApicalPreparation Of Root Canals With Three SetsOf Dedicated Instruments6,074,209JohnsonJun. 13, 2000Reduced Torque Endodontic File6,217,335Riitano et al.Apr. 17, 2001Endodontic Systems And Methods For TheAnatomicall, Sectional And ProgressiveCorono-Apical Preparation Of Root CanalsWith Minimal Apical Intrusion6,267,592MaysJul. 31, 2001Highly Flexible Instrument For DentalApplications6,312,261MaysNov. 6, 2001Endodontic Obturator With RemovableCarrier And Method Of Use Thereof6,315,558Farzin-Nia et al.Nov. 13, 2001Method Of Manufacturing SuperelasticEndodontic Files And Files Made Therefrom6,390,819RiitanoMay 21, 2002Endodontic Systems And Methods For TheAnatomical, Sectional And ProgressiveCorono-Apical Preparation Of Root CanalsWith Dedicated Stainless Steel InstrumentsAnd Dedicated Nickel/Titanium Instruments6,419,488McSpadden et al.Jul. 16, 2002Endodontic Instrument Having A Chisel Tip6,514,076Bleiweiss et al.Feb. 4, 2003Precipitation Hardenable Stainless SteelEndodontic Instruments And Methods ForManufacturing And Using The Instruments6,520,774MaysFeb. 18, 2003Highly Flexible Instrument For MedicalApplications6,644,972MaysNov. 11, 2003Endodontic Obturator With RemovableCarrier And Method Of Use Thereof6,746,245Riitano et al.Jun. 8, 2004Methods For Cleaning And ShapingAsymmetrical Root Canals In An AnatomicalFashion2004/0121283MasonJun. 24, 2004Precision Cast Dental Instrument2003/0077553BrockApr. 24, 2003Endodontic Instrument Having NotchedCutting Surfaces2004/0058297DangerMar. 2, 2004Root Canal Instrument2004/0043357GarmanMar. 4, 2004Endodontic Instrument2004/0023186McSpaddenFeb. 5, 2004Multi-Tapered Endodontic FileRe. 34,439HeathNov. 9, 1993Dental Compactor Instrument